Besides methods using perchlorinated or trichlorinated solvents, one of the most commonly used methods to degrease wet skins is treating these skins with organic solvents and non-ionic and/or anionic detergents in a drum in an aqueous environment to emulsify fats. DE-OS 25 22 902, for example, describes degreasing compositions containing non-ionic and/or anionic surfactants as auxiliaries in an alcohol-based solvent. WO 93/18188 describes the use of degreasing agents based on non-ionic emulsifiers of the fatty alcohol alkoxylate type for degreasing skins, hides, and leathers. Said non-ionic emulsifiers contain a mixture of (a) C12-C18 fatty alcohol ethoxylates with an average of more than 6 EO groups in the molecule and (b) first-runnings fatty alcohol ethoxlates with more than 3 EO groups in the molecule, with (i) the fatty alcohols on which components (a) and (b) are based having an iodine number of under 10 and (ii) component (b) being present in a quantity of 2 to 10% by weight, in relation to the sum of (a) and (b).
A major disadvantage of these processes, however, is that the generated waste water will contain detergents, fats, and salts which are difficult to biodegrade and/or recycle. Another disadvantage is that the result reached by this method is not as efficient as with methods using perchlorinated or trichlorinated solvents.
Another degreasing method for wet skins is to treat these skins with hydrocarbons, such as derivatives of petroleum, white spirit, and nonyl phenol. A disadvantage of these degreasing methods is that water does not dissolve in the solvents employed. Hence the skins have to be dried in a separate process step. Besides, with said degreasing methods highly polluted waste water is generated comprising int. al. fats, hair, flesh remains, salts, and hydrocarbons. Dry skins, on the other hand, are generally degreased by using chlorinated solvents such as PER (tetrachloroethylene) and TRI (trichloroethylene). However, these solvents are known to be highly undesired in respect of human health as well as from an environmental point of view.
Processes for drying skins are for example described in U.S. Pat. No. 3,444,625. This document relates to processes in which water is removed from water-containing hides and skins by extraction with organic solvents such as, for example, formal, acetone, chloroform, or dichloromethane. A disadvantage of these processes, however, is that the skins have to be degreased in a separate step.